1. Field of the Invention
The present invention concerns an accessory for a flap. The accessory is used to cover the valve passage opening in the rim of a wheel. More particularly, it is normally used in an assembly consisting of a wheel rim, a flap, an inner tube, and a tire. The accessory prevents the flap from creeping into the valve passage opening over time, or even under severe operating conditions.
2. Description of Related Art
Tires with an inner tube require the use of a flap. As is known, a flap is an elastomer protection ring arranged between the inner tube on one side and the bottom of the rim groove and the tire beads on the other side. The flap prevents the inner tube from being pinched between the rim and the beads; it protects the inner tube from contact with or rubbing against the rim. This is particularly useful because a wheel rim can reach quite high temperatures during rolling, bearing in mind the proximity of the braking mechanism.
One of the problems associated with the use of a flap results from its creeping through the valve passage orifice present in the rim under the action of the pressure exerted by the inner tube combined with the heat from the brakes; in effect, it is found that under these conditions the flap becomes progressively squeezed through said orifice. This mechanism generally induces a local thinning of the flap in the area of the valve orifice; it follows that the valve stem, which is then displaced in the direction of the rim, risks coming into frictional contact with the brake drum with easily imaginable consequences.
To prevent the flap from creeping into the valve passage orifice, patent FR 2 177 645 proposes a reinforcement assembly consisting on the one hand of a rigid insert, for example made of a plastic material, which is fitted into the orifice of the flap designed to allow passage of the valve and forms the inside wall thereof, and on the other hand a layer of reinforced elastomer mix that forms a lining of the radially inside surface of the flap all round said insert. The rigid insert and the reinforced elastomer layer restrict the creep of the flap into the rim""s valve passage orifice; in addition, the insert prevents displacement of the valve stem towards the brake drum. However, this solution proposing the use of an elastomer layer is not satisfactory when the conditions under which the tire provided with the reinforcement assembly in question is used result in heating of the flap to temperatures above 90xc2x0 C. to 100xc2x0 C., a temperature range in which the elastomer itself undergoes creep. On the other hand, the production and then fitting of said assembly to its flap turn out to be complex because numerous steps are involved: molding and then positioning of the insert, production of the reinforced elastomer layer and then its bonding to the flap, for example by means of a press.
The aim of the present invention is to propose a flap accessory which does not suffer from the drawbacks of the state of the prior art and which, in particular, makes it possible to restrict or eliminate the creep of the flap into the valve passage orifice. The flap accessory according to the invention is a molded element comprising a base of essentially oblong shape with one face designed to be in contact with a flap in the fitted position and a hollow, cylindrical insert projecting from said face of said base, said base being provided with an orifice at the end of the insert to allow the passage of an inflation valve stem through the insert. In addition, the accessory according to the invention is formed in one piece from a moldable, thermally resistant material, i.e. a material which can resist temperatures up to at least 180xc2x0 C. without showing virtually any creep as a function of time.
This good temperature resistance makes it possible to prevent creep of the flap with time and prevents said flap from moving partly into the valve passage orifice of the rim, even if elevated temperatures are reached as a result of especially severe rolling conditions, in particular repeated braking.
The flap accessory according to the invention is preferably made from a plastic material, in particular polyamide.
The base of said accessory is in the form of a thin plate designed to be inserted between the rim and the flap and having an area such that said plate covers the rim valve passage orifice and extends beyond the orifice on all sides. As for the cylindrical insert, this is designed to be inserted with a push fit into the cylindrical valve passage orifice provided in the flap, forming the inside wall thereof while ensuring contact between the plate forming the base and the flap itself and keeping said base in position regardless of the forces imposed respectively on the flap and on the rim. xe2x80x9cPush fitxe2x80x9d means that the insert is introduced into the flap by deforming the flap elastically so that said flap exerts radial forces on the insert in order to hold the latter firmly in the flap.
Advantageously, the material constituting the base of the accessory should confer upon said base an appropriate longitudinal bending flexibility so that the base can deform as far as necessary to follow the rounded shape of the flap.
In a variant embodiment, the base of the accessory is provided on its face intended to be in contact with the flap, with ribs or relief projections extending transversely relative to the major dimension of the base and across the whole of the minor dimension; these ribs or projections, which may or may not be regularly spaced, are designed to reduce or prevent creep of the material constituting the flap parallel to said base, and to confer upon the base a greater bend rigidity about an axis extending essentially in the direction perpendicular to the direction of the ribs.
To facilitate the passage of the valve stem through the insert at the time of fitting or removal, the insert according to the invention is provided with at least one opening having appropriate dimensions, formed in the area of its connection to the base.